For the most part, efforts to solve the problem of global warming have focused on the strategy of mitigation. The idea is to reduce the amount of greenhouse gases we put in the atmosphere by changing, as a species, our cultural and industrial habits. But conjuring the political will to actualize such change on a global scale is - to put it politely - a slow and complicated process.

Some researchers have turned to more radical proposals. Geoengineering refers deliberate large-scale manipulations of the environment - land, water and/or atmosphere - to affect the Earth's climate and counteract global warming. Seems risky, doesn't it? It is. We take a look at five audacious geoengineering concepts.

Virtual Volcanoes

Geoengineering is a legitimate area of research, but generally speaking, the scientific community recognizes the extreme danger of deliberately tinkering with the planet. After all, look what we've done inadvertently. What would happen if we actually tried to change the climate?

At a 2015 European Geosciences Union General Assembly Just last week, more than 11,000 scientists gathered to discuss, among other things, the perils of atmospheric engineering. One of the big topics concerned a climate engineering concept with a relatively long history and a bit of current momentum - shooting artificial volcano ash into the stratosphere.

Researchers who have studied the geological record have noted that major volcano eruptions, ironically, tend to cool down the planet. That's because volcanoes throw millions of tons of sulfur dioxide aerosols into the stratosphere, which in turn act like a sunscreen, bouncing sunlight back into space. Over the years, proposals have been put on the table to shoot such aerosols into the stratosphere with aircraft, rockets, balloons and even massive artillery guns.

Space Parasols

Stratospheric aerosols are just one of several proposals to create a kind of planetary sunshade over the Earth, an idea often termed solar radiation management (SRM). Some of the other concepts are delightfully literal. The illustration above depicts a giant space lens placed between the Earth and the sun, designed to diffuse a specific percentage of solar energy from reaching the planet, thus cooling things down and balancing out the greenhouse effect.

As you might suspect, towing an enormous lens into space presents some logistical hassles. Other proposals include deploying a cloud of millions of smaller space lenses, mirrors or even tiny self-propelled spacecraft somewhere between the Earth and the sun. Or if you really want to get tricky, why not a parasol of lunar glass?

Flood Death Valley?

Then there are the proposals that aim to treat the symptoms, so to speak. Anthropogenic climate impact is suspected of contributing to all sorts of unfortunate developments around the planet, from melting icecaps to the current drought in the western United States.

One unusual proposal could potentially solve both problems. The idea of flooding Death Valley with seawater is a notion that occasionally pops up online, although no serious studies have been made. The intent is to counter rising seawater levels in populated coastal areas by draining the seawater inland via a massive canal from the Pacific Ocean to, say, Death Valley. It would require an unprecedented feat of construction and technology, but geoengineering is not for the faint of heart. And we're not even going to mention the idea to wrap glaciers in blankets.

Artificial Forests

Fields of air scrubbers would work like forests of artificial trees, pulling carbon dioxide out of the air. Credit: Institution of Mechanical Engineers

Trees help combat global warming by absorbing the excess carbon dioxide we're pumping into the atmosphere and converting it into oxygen. But unfortunately, there aren't enough trees on the planet to handle all the CO2 that's warming the atmosphere, triggering the greenhouse effect, and rattling the climate.

But what if we could build more efficient artificial trees? That's the basic idea behind the research of physicist Klaus Lackner, director of the Lenfest Center for Sustainable Energy at Columbia University. His carbon dioxide air extraction devices may not look like trees, but they work in a similar fashion, pulling carbon dioxide out of the air in a process called engineered chemical sinkage.

Compressed into a liquid, the carbon dioxide could be stored underground in reservoirs and aquifers using existing technology. Individually, Lackner's air scrubbers are many times more efficient than trees, but we'd still need a lot of them. The concept of artificial forests might seem extreme, but maybe we could place one next to Death Valley Lake, for purposes of grim irony.

Mediterranean Dam

Our current global warming crisis has triggered a tidal wave of new geoengineering research, much of it processed through sophisticated computer modeling programs. But bold schemes to sculpt the planet go back quite a ways. One of the most audacious proposals was put forth by German architect Herman Sörgel in the 1928.

His plan? To build a massive hydroelectric dam across the Strait of Gibraltar, lowering the level of the Mediterranean Sea more than 500 feet. The rather ambitious project would create vast new tracts of land for agriculture and settlement, along with a roadway connecting Sicily to Tunisia, an irrigation canal to the Sahara desert, and an enormous new source of hydroelectric energy to make it all happen.

One nice thing about the Germans, they think big. Sörgel's plan eventually became the basis of the larger Atlantropa movement to unite Europe and Africa, which had Utopian ambitions despite its many dubious geopolitical elements. (No one bothered to ask the existing Mediterranean coastal communities what they thought of the plan.) Still, Sörgel had the planet's best interests at heart. War, not climate change, was the existential threat of the era and Sörgel was hoping geoengineering could provide a solution.